As integrated circuit fabrication techniques continue to decrease into deep-submicron processes, the supply voltages for powering devices made by these techniques continues to decrease. Moreover, in order to extend battery life for portable devices (such as, for example, mobile terminals) there is a strong motivation for lowering power consumption.
To this end, there can be motivating reasons for having a plurality of voltage supplies on a chip, each of which may be selected through one or more selection signals. For example, it may be useful to have a selectable voltage supply in order to meet or exceed a circuit's performance specifications. Also, it might be useful to select between two or more supplies for a specific circuit, choosing a supply according to the operation mode, or perhaps to reduce power consumption. Such an approach can involve a programmable on-chip switch to select a desired voltage. For proper operation, the switch should be able to handle the different voltages and different turn-on/turn-off times of the different supplies. If the timing is not properly taken into account, large substrate currents could flow and result in the latch-up of a device.
A conventional selectable voltage supply may use switches implemented with large PMOS transistors. If the voltage differences between the supplies are large, the parasitic diodes of the PMOS transistors can conduct. This can lead to large parasitic currents which can cause a variety of breakdown phenomena of the transistor devices.
Accordingly, there is a need for a voltage supply selector which can select a particular voltage supply while eliminating leakage currents to ensure proper functioning of the integrated circuit device.